1. Field of the Invention
The present invention relates generally to a one-way clutch that includes a bearing block for supporting at least one rotational member. More particularly, the present application involves an overrunning clutch that includes a bearing block mounted to a pedestal that engages a race of the clutch to achieve integral piloting and reduced wear.
2. Description of the Prior Art
Rotational power transmission devices, such as torque converters and other automotive transmission components, function to impart torque from one shaft to another shaft when desired. These devices use roller one-way clutches (OWC) extensively. As components in transmissions, roller one-way clutches allow for smooth transitions from one torque path to another as the transmission shifts through its operating ranges. Typically, this is achieved by preventing the rotation of an element of a planetary gear set or by allowing for relative rotation between members of the gear set. In torque converters, the OWC locks up the stator during vehicle launch, when there is a high speed differential between the impeller and the turbine, and redirects the fluid flow into the impeller, improving the efficiency of the converter. When the vehicle is coasting and the speed differential between the impeller and turbine is reduced, the OWC allows the stator to free-wheel or overrun. In this condition, torque is no longer transferred across the OWC. One-way clutches used in torque converters operate in a high temperature environment (100°-120° C.) for a significant portion of their operation. Imbalances inherently present in the stator assembly result in radial inertial loads that are active during the overrunning portion of the duty cycle for the clutch. During this stage, the components of the OWC rotate relative to one another; consequently, clutch elements are needed that act as journal surfaces, supporting and centering the rotating components.
Known torque converter (stator) clutches 10 are disclosed with reference to FIGS. 1 and 2. The clutch 10 includes rollers 100 that are urged by energized springs 102 to be in contact with an inner race 12 and an outer race 14 that is installed in a stator 44. The springs 102 are supported by pedestals 16 that extend from the outer race 14. Movement of the components in the axial direction 104 is prevented through the use of features on the stator 44 as well as other components such as retainers 110 and/or circlips in the clutch 10 assembly. Fluid exiting a turbine portion of the converter impinges upon blades of the stator 44 and drives the stator 44 and the outer race 14 installed within to rotate in a counterclockwise direction about an axis of revolution 98 of the clutch 10. In turn, the rollers 100 are rotated into a locking position between the inner race 12 and the outer race 14. The reaction of the stator 44 against the inner race 12 serves to add to the torque delivered to the resulting turbine output shaft. Alternatively, when the relative slip between the turbine and impeller in the torque converter 10 is low or zero, the fluid exiting the turbine vanes or blades strikes the opposite side of the blades of the stator 44 and causes the stator 44 to freewheel.
In a conventional stator clutch the rotation of the inner race relative to the rest of the assembly in the overrun mode, in order to maintain concentricity of the components (piloting), is made possible, in the embodiment shown in FIG. 1, and particularly FIG. 1C, through the use of bearing surfaces 110A, 44A that are machined directly onto the stator 44 on one end and on to the retainer 110 at the opposite end. Pedestals 16 therefore do not come into contact with the surface of inner race 12. The machining of these surfaces with the tight tolerances mandatory for piloting is expensive; additionally, the overall length of the stator assembly has to be increased to accommodate the lengths of these bearing surfaces. In the clutch 10 illustrated in FIG. 2, the internal surface of the pedestals 16 are used in place of the machined stator and retainer surfaces described with respect to FIG. 1, in order to maintain concentricity and also achieve more compact sizes. This allows for a smaller envelope for the clutch 10 assembly without sacrificing stator performance.
In order to minimize frictional losses and wear on the inner race 12 in overrun mode, the pedestals 16 are coated with manganese phosphate. The phosphate coatings are applied following a grinding of the inner surfaces of the pedestals 16 and are applied to the entire internal surface of the outer race 14, including pedestal 16 and working surfaces. Shot blasting is then performed on the working surfaces of the outer race 14 to remove the phosphate coating therefrom. Aside from the time and expense necessary to apply the manganese phosphate coating, this design may be problematic in that it may be difficult to ensure complete removal of the coating from active surfaces of the outer race 14. The coating process may not be easily integrated into a production environment, and may not perform well enough to meet the requirements necessary in applications that require high durability in which high overrun speeds and greater imbalance loads are present on the stator 44 resulting in a breakdown of the phosphate coating over time and a resulting contamination of hydraulic fluid in the torque converter.
One known example of an overrunning clutch is described in Johnson, et al., U.S. Pat. No. 3,732,956, the entire contents of which are incorporated by reference herein in their entirety for all purposes. This design features an overrunning roller clutch that has an inner race and an outer race with a caged roller sub-assembly located radially therebetween. The caged roller sub-assembly cooperates with the inner and outer races to permit them to rotate relative to one another in one direction while locking them together in response to relative rotation in the opposite direction. The springs, rollers, and bearing blocks are retained within the caged sub-assembly. The caged sub-assembly is made of a series of stamped metal segments that are connected to one another in series. Although capable of forming an overrunning roller clutch, the caged sub-assembly and resulting components are complex in nature and include many operating parts.
Yamamoto, et al., U.S. Pat. No. 7,080,721, discloses a clutch mechanism which includes the use of a block bearing extending between the inner and outer races. These block bearings are removable, unitary devices which extend entirely between the races. The block bearings are not functionally associated with the clutch rollers or springs, but serve only a piloting function. No pedestals integrally formed with either race are disclosed which are associated with the piloting function.
Another overrunning clutch assembly is disclosed in King, et al., U.S. Pat. No. 4,679,676, the contents of which are incorporated by reference herein in their entirety for all purposes. This overrunning clutch features a concentric control cage that maintains an inner race and outer race in a co-axial arrangement with one another. The control cage includes a cage body and a pair of metal end rings. For assembly purposes the control cage is a single unitary structure but in operation functions as if the control cage is made of a plurality of separate pieces connected to one another. A plurality of journal blocks are included in the cage body with lower surfaces that engage the inner race during overrun. The cage body and journal blocks are made of a plastic material with desirable frictional characteristics. Double side rails are present in order to circumferentially interconnect the journal blocks and extend around the entire circumference of the cage body. The disclosed arrangement accounts for thermal expansion within the clutch assembly between the different components made of different materials and geometries during operation of the overrunning clutch. Although capable of working for its intended purpose, the above disclosed designs include a high number of complex molded parts. The use of the cage body in a one way clutch assembly requires the sacrificing of the axial length of the rollers thus resulting in an overall lower torque carrying capacity. This sacrifice may be problematic in the context of a compact torque converter one way clutch design. The use of a caged spring and roller system introduces additional complexity with regards to assembly automation. As such, there remains room for variation and improvement in the art. The invention described here seeks to address these shortcomings described. The strength of the current invention lies in its simplicity, ease of assembly and facility for use in compact environments.